A wireless communication system has a configuration shown in, e.g., FIG. 1. In the wireless communication system, transmitting and receiving stations 101, 102 and 103 move to build a particular network (an ad hoc network) and share information even though a base station (not shown) or an access point is not present. In the ad hoc network, in response to the travel of the transmitting and receiving stations 101, 102 and 103, the communication is always maintained by determining a communication target and relay status in accordance with the traveled position and the line status.
FIG. 2 is a view showing a schematic configuration of a wireless communication device of the transmitting and receiving stations 101, 102 and 103. In FIG. 2, a wireless communication device 200 of the transmitting and receiving stations 101, 102 and 103 includes an antenna 201, a transmitting unit 202, a receiving unit 203, a physical layer processing unit 204, MAC (Media Access Control) layer processing unit 205 and IP (Internet Protocol) layer processing unit 206. The wireless communication device 200 is electrically connected to a router 210.
As for the flow of transmission data, the wireless communication device 200 performs the relay of the transmission data outputted from a terminal such as a PC (Personal Computer). An IP packet outputted from the router 210 is inputted to the wireless communication device 200 and routed in the IP layer processing unit 206. In a case where the IP packet is routed to another transmitting and receiving station, a MAC frame is generated from the IP packet in the MAC layer processing unit 205. At the same time, in the MAC layer processing unit 205, a wireless channel is obtained by an autonomous distributed control. When the wireless channel is obtained, the wireless communication device 200 modulates the MAC frame information in the physical layer processing unit 204, and transmits the modulated information from the transmitting unit 202 through the antenna 201.
As for the flow of reception data, a signal received by the receiving unit 203 through the antenna 201 is demodulated in the physical layer processing unit 204 and then inputted to the MAC layer processing unit 205 as the MAC frame information. The MAC layer processing unit 205 checks a destination address and a frame error and confirms whether or not it is in a response order of itself. If the response is in its own response order, the MAC layer processing unit 205 generates a response frame for a previously received MAC frame to send the response frame as a reply. At the same time, the MAC layer processing unit 205 delivers an IP packet to the IP layer processing unit 206. The IP layer processing unit 206 determines whether to discard the data or output the data to the router 210 based on the routing information.
FIG. 3 is a timing chart for explaining an operation of the wireless communication system. In FIG. 3, a propagation delay rate is set to be almost the same as a symbol rate and the number of the transmitting and receiving stations (nodes) is three. An address code is previously set. The address code is set as address code information in the IP layer processing unit 206 and the MAC layer processing unit 205 of the wireless communication device 200. In the set address code information, while using the address code as a key, the number of subscriber stations and a response number are stored as a pre-assignment table.
Nodes ‘A’, ‘B’ and ‘C’ have a previously determined response order when a response is requested. In FIG. 3, a response order (1) is the highest in priority and a response order (3) is the lowest. In the same communication system, different nodes do not have the same response order. FIG. 3 shows a case where the transmission of route information and data is started after a carrier sense is performed from the node ‘A’ (after a fixed waiting time).
When the “route information and data (data representing information of voice, image and the like)” is transmitted from the node ‘A’, each receivable node performs reception of the “route information and data” transmitted by the node ‘A’. Here, the reply of another node is available when the reception of the “route information and data” is completed at the corresponding node. Among the nodes performing the reception of the “route information and data”, first, if the node ‘B’ having the response order (1) completes the reception of the “route information and data”, the node ‘B’ sends a “route information and ACK” as a reply. Among the nodes which have received the “route information and ACK” of the node ‘B’ and have lower response orders than that of the node ‘B’, one having the highest response order, i.e., the node ‘A’ having the order next to that of the node ‘B’, transmits a “route information and ACK”. Here, the node ‘A’ is a transmission source that has transmitted “route information and data” at the beginning. The node ‘A’ urges other nodes having lower response orders to transmit the “route information and ACK”. Although the node ‘A’ is the transmission source, the node ‘A’ transmits “route information and ACK” to maintain the route.
In this manner, each node transmits “route information and ACK” when it receives “route information and ACK” of a node having an immediately higher response order. Each station determines whether or not the response order is its own order by judging its own response order from information related to response orders of reception terminals included in the route information of the node ‘A’ that has transmitted “route information and data” at the beginning, and further, by judging whether the number of received responses counted up by a communication control unit or information representing response order of the transmission source including ACK corresponds to its own response order.
When receiving a reply from the node ‘C’ having the lowest response order, the node ‘A’ as the transmission source transmits “route information and termination” to notify the termination of the communication. At this time, by checking a response order included in ACK, it is determined whether the transmission has come from a transmitting and receiving station having the lowest priority or whether the number of receptions is equal to the number of subscriber stations (in this case, 3). The above process is the basic operation.
A pre-assignment method has a constraint condition that the method is applicable to only nodes capable of communicating within 1 hop, i.e., direct communication. That is to say, even if nodes have been registered in a pre-assignment group, for example, as can be seen in FIG. 4, in a case where the nodes ‘A’ and ‘C’ cannot perform direct communication and relay is required, the pre-assignment method is not available. The transmission and reply of the nodes ‘A’ and ‘C’ do not reach each other.
As a prior art, for example, Patent Document 1 discloses a technique that efficiently specifies the operations of an IP address and a MAC address of a wireless network by an ad hoc routing protocol.
Patent Document 1: Japanese Patent Application Publication No. 2013-110521
In the aforementioned prior art, there are constraints as follows: a pre-assignment communication is available only when the direct communication is possible; and the same address code information is set and kept by a manager or the like in all wireless devices belonging to an ad hoc network. In a case of having the same address code, if the number of subscriber stations and response numbers are different, the communication is not possible.
Moreover, in an ad hoc network where participation and departure of communication subjects are frequent, it is difficult for a manager to maintain the above constraints and to set and manage the most efficient address information while judging whether or not direct communication is possible.